Dual piston cylinder



Oct. 18, 1960 H. c. MALPASS DUAL PISTON CYLINDER 2 Sheets-Sheet 1 FiledJuly 5, 1955 Oct. 18, 1960 H. c. MALPASS DUAL PISTON CYLINDER 2Sheets-Sheet 2 Filed July 5, 1955 INVENTOR .5447: 6 4579055 BY ATTORNEYUnited fates atent DUAL PISTON CYLINDER Harry C. Malpass, Ferndale,Mich, assignor to General Motors Corporation, Detroit, Mich., acorporation of Delaware Filed July 5, 1955, Ser. No. 519,783

'4 Claims. (Cl. 12138) This invention relates to dual piston cylindersin general and more particularly to hydraulically actuated dual pistoncontrol cylinders.

The use of cylinder means including a pair of piston heads secured to asingle shaft and disposed in separate work chambers is well known andaccepted as a means for providing a control cylinder having an increasedWork capacity without appreciably changing the cylinders dimensions. Inthe past, such dual piston cylinders have been actuated by pneumaticfluids. The adaptation of such cylinders for use with hydraulic fluidshas not proven very successful in view of problems incident toachievingan immediately responsive advance and a full retraction despite theincompressible nature of the hydraulic fluid.

It is now proposed to provide a compact dual piston cylinder assemblyadaptable for use within a hydraulic fluid control system as well as apneumatic fluid control system. It is proposed to provide a simple andefiective means for introducing the working fluid simultaneously to eachworking area in order to provide dual piston cylinder means immediatelyresponsive to a full working pressure. It is further proposed to includemeans providing against the trapping of hydraulic fluids such as wouldretard or prevent a full advancing stroke of the piston means due to theincompressible nature of a hydraulic fluid. It is still further proposedto provide means for a more responsive return stroke of the piston meansthan has previously been provided in similar piston control means.

In the drawings:

Figure 1 is a cross-sectional side view of a dual piston hydrauliccontrol cylinder embodying the present invention.

Figure 2 is an end View of the dual piston hydraulic cylinder shown inFigure 1 taken in the plane of line 2-2 and viewed in the direction ofthe arrows thereon.

Figure 3 is a cross-sectional side view of a modified form of theproposed dual piston hydraulic control cylinder.

Referring first to Figures 1 and 2, the present invention is shownembodied within a hydraulically actuated welding gun head which isadapted to have secured to one end thereof a welding electrode, which isnot here shown. There is provided a cylinder having an enlarged bore 12provided near one end thereof and a smaller bore 14 near the other endthereof. Stepped shoulders 16 and 18 are provided between the enlargedand smaller bores. A gland member 20 is disposed within the end of theenlarged bore 12 and abuts against the one shoulder 16 to lie adjacentthe end of the smaller bore 14. The gland member 20 is formed to receiveinternal and external O-rings 22 and 24 for fluid sealing. The glandmember 20 includes integrally therewith a sleeve portion 26 extendedwithin the enlarged bore 12.

Dual piston means 28 are provided within the cylinder 10 and include apiston rod 30 having a first piston head 32 secured to one end thereofby a lock washer 34 and nut means 36 threaded upon the one end thereof.The piston head 32 is formed to receive internal and external O-rings 38and 40 for fluid sealing. The first piston head 32 is disposed withinthe smaller cylinder bore 14. A second piston head 42 is provided uponthe piston rod 30 within the enlarged bore 12 and is formed to receivean external O-ring 44 for fluid sealing.

The gland member 20, which forms a dividing wall between piston heads 32and 42, is secured within the enlarged bore 12 by means of a bushingmember 46, bushing retainer 48 and snap ring 50. The bushing member 46includes apertures 52 and 54 provided therein and adapted to receiveears 56 formed from the bushing retainer member 48 and bent inwardly.The bushing retainer member 48 also includes external ears 58 receivedwithin slots 60 provided in the end of the cylinder member 10. Theinternal and external ears 56 and 58 of the bushing retainer member 48provide means for holding the bushing member 46 in fixed position.

The outer end of the piston rod member 30 is formed to provide flatsurfaces 62 which are engaged within the bushing member 46 having anopening 64 formed therethrough which is complementary to the shape ofthe end of the piston rod. The bushing member 46 being retained itselfis adapted to restrain rotation of the piston rod member 30.

The cylinder member 10 is provided at its other end with a neckedportion 66 having threads 68 formed externally near the end thereof toprovide means for securing the cylinder to a supporting structure, nothere shown. The necked portion 66 is formed to provide a passage 70which is internally threaded near one end as at 72 to receive ahydraulic fluid line, not here shown. The passage 7 ti communicates witha first work chamber 74 formed above the first piston head 32 which isadapted to receive the nut and washer fastening means 34 and 36therewithin. A secondary or auxiliary inlet passage 76 is formed throughone side of the cylinder 10 in communication with the first work chamber74 and is internally threaded, as the other passage 70, to receive ahydraulic fluid line, not here shown. Either fluid passage 70 or 76 maybe used depending upon which is the more accessible when the cylinder 10is installed in a welding jig; the other opening then being closed.

The piston rod 30 is formed to provide a passage 78 centrallytherethrough which communicates through an aperture 80 with the secondwork chamber 82 between the second piston head 42 and the gland member28. The gland member 28 is undercut as at 84 about the piston rod anddirectly over the second piston head to provide more directcommunication through aperture 80 with the second work chamber 82. This,as will be described, enables simultaneous pressure application in bothwork chambers.

The space or chamber 85 between the first piston head 32 and the glandmember 28 is, in the present instance, adapted to receive a workingfluid for backing ofl or retracting the piston means 28. For this reasonan opening 80 is formed through the side of cylinder 10 and a fitting 88is provided thereover. The fitting 88 is threaded to receive a fluidline, not here shown. During the advance stroke of the piston means 28fluid is exhausted from chamber 85 and during the retraction strokefluid pressure is built up therein. g

The second piston head 42 is secured to the piston rod so that there isa space provided between thesecond piston head and the gland when thefirst piston head is in the fully retracted position. This space enablesmore direct communication with the passage 78 provided in the piston rod30 and allows more ready escape of the hydraulic fluid from such spacethrough aperture 80 in communication therewith when the piston means arebeing retracted.

. The grooves 90 and 92 at the ends of the enlarged bore 12 and smallerbore 14 are incident to machining operations. The groove 94 about theunderside of piston head 32, however, is provided to accommodate theworking fluid when the piston head is in its advance position and readyto be retracted. That is, fluid entering opening 86 has direct access tothe annular space provided by groove 94 and the pressure is immediatelybuilt up against piston 32 to start the retraction of the piston meansand upon a breaking away of the piston 32 from gland 20 the entireunderside of the piston is acted upon by the retracting work fluid.

Referring now to Figure 3, there is shown a modified hydraulic dualpiston structure. Those parts which are basically similar to thecylinder means of Figures 1 and 2 are not rcdescribed.

The cylinder member 100 includes a bore 102 enlarged near the lower endthereof as at 104. The gland and sleeve member 106 is received withinbore 102 and is formed to provide a flange or collar 1% about the end ofthe sleeve which engages the shoulder 110 formed at the end of the bore104. The chamber 112 between the first piston head 32 and the glandmember 106 is exhausted by passage means 114 formed within the glandmember and communicating with an opening 116 formed through the side ofthe cylinder member. The annular groove 118 provided around the glandmember 106 facilitates assembly of the external O-ring 120 providedabout the gland member and the O-ring provided about piston head 32. Thebushing member 122 is retained within the end of the cylinder member byset screw means 124 and a snap ring 126.

In the embodiment of Figure 3, the second piston head 42 is spacedsufliciently apart from the gland member 106 to provide communicationbetween the aperture 128 provided at the end of the piston passage 130and the second work chamber space, designated 132. The sleeve portion ofgland member 106 is undercut as at 134 in the course of machining aSquare corner edge at the end of chamber 132.

The operation of the proposed dual piston hydraulic control cylinder isessentially the same for the embodiments shown by Figures 1 and 3. Theoperation of the embodiment of Figure 1 will be described in detail withspecific differences as to the structure of Figure 3 mentionedgenerally.

A working fluid is received within the first work chamber 74 and, bymeans of passage 78 provided through the piston rod 30, within thesecond work chamber 82. The working fluid is immediately available forwork upon both piston heads 32 and 34. Fluid access to the second workchamber is provided by undercutting the gland, as at 84, to providedirect communication with piston rod passage 78 in the structure ofFigure 1, and in the embodiment of Figure 3, by spacing the secondpiston head 42 to permit direct communication between piston rod passage130 and chamber 132.

The pressure of the working fluid advances the piston means 28 while theworking fluid in chamber 85, used to retract the piston means, isexhausted through opening 86 and the air within the space below thesecond piston head 42 is exhausted through the apertures 52 and 54provided in bearing member 46. In the structure of Figure 3, air ventsmay be provided in the bushing member or the fit between the end of thepiston rod and the bushing member may be such as will allow the escapeof such air.

To prevent an undesirable build-up of pressure within chamber as thefirst piston head 32 nears the end of its stroke, the first piston headmay be undercut as at 94 to provide increased communication with thepassage means permitting the exhaust of fluid from such chamber space.

The piston means are retracted by exhausting the working fluid fromchambers 74 and 82, in the reverse manner as applied, and by introducingfluid under pressure through opening 86 into chamber 85 to act againstthe under surface of piston head 32.

I claim:

1. A dual piston hydraulic cylinder comprising a cylinder member havinga closed end, a sleeve member disposed within the open end of saidcylinder and having a transverse annular wall provided at one endthereof and dividing said cylinder into spaced chambers, a piston shaftdisposed within said cylinder and extended through said wall, pistonheads secured to said shaft in each of said chambers, fluid passagemeans formed centrally through said piston shaft and in opencommunication with each of said chambers on similar sides of said pistonheads, means provided between said transverse wall and said piston headin said chamber adjacent said open end of said cylinder member toprevent cutting olf said fluid passage means when said last named pistonhead is in a position adjacent said transverse wall, first fluidinletmeans disposed in the closed end of said cylinder and communicat ingdirectly with the adjacent face of one of said piston heads andcommunicating with the corresponding face of a second of said pistonheads through said fluid passage means in said piston shaft forpressu'rizing said piston heads simultaneously and advancing said pistonheads and said piston shaft in the direction of the open end of saidcylinder member, second fluid inlet means disposed in the side wall ofsaid cylinder member and communicating with the chamber formed betweensaid transverse annular wall and said piston head disposed in saidchamber adjacent said closed end of said cylinder member to allow fluidto enter said chamber and pressurize only the face of said piston headadjacent said transverse wall to retract said piston heads and saidpiston shaft in the direction of the closed end of said cylinder memberand means for retaining and locating said transverse wall within saidcylinder.

2. The dual piston hydraulic cylinder of claim 1 wherein said meansbetween said transverse wall and said piston head in said chamberadjacent the open end of said cylinder member includes an undercut inthe face of said transverse wall adjacent said last named piston head topermit direct communication between said work chambers via said passagemeans in said piston shaft when said piston heads are in a retractedposition.

3. The dual piston hydraulic cylinder of claim 1 having said piston headadjacent the closed end of said cylinder member undercut to permitpressurizing said piston head when said piston head is in a fullyadvanced position.

4. A dual piston hydraulic cylinder comprising a cylinder member havingone end closed, a sleeve member disposed within the open end of saidcylinder and having a transverse annular wall provided at one endthereof and dividing said cylinder into opposite chambers, a pistonshaft disposed within said cylinder and extended through said wall,piston heads secured to said shaft in each of said chambers, fluidpassage means formed centrally through said piston shaft and in opencommunication with each of said chambers on similar sides of said pistonheads, first fluid inlet means disposed in the closed end of saidcylinder and communicating directly with the adjacent face of one ofsaid piston heads and communicating with the corresponding face of asecond of said piston heads through said fluid passage means in saidpiston shaft for providing entrance of fluid to pressurize said pistonheads and move said piston heads and said piston shaft toward the openendof said cylinder member, a fluid inlet opening through the side wallof said cylinder member and in said transverse wall, fluid passage meansbetween said fluid inlet opening and said chamber adjacent the closedend of said cylinder member, said fluid inlet opening and said lastnamed passage providing for the entrance of fluid into said last namedchamber and between said transverse wall and said one piston head forpressurizing the face of said piston head adjacent said transverse walland moving said piston heads and said piston shaft toward the closed endof said cylinder member, said piston head received within the chamberadjacent the open end of said cylinder spaced apart from said transversewall to prevent cutting 01? said fluid passage means upon fullretraction of said piston shaft, and a bushing member secured in theopened end of said cylinder member and abutting said sleeve member toretain said sleeve member in said cylinder member and to locate saidtransverse wall within said cylinder member.

References Cited in the file of this patent UNITED STATES PATENTSFOREIGN PATENTS Great Britain Feb. 17, 1938

